Sheet-gripper mechanism of printing machines



June 22 1926.

J. w. JAKEMAN SHEET GMPPER NEGHANISN oF PRINTING MACHINES Filed Feb' 51925 f5 Sheets-Sheet- 1 June 22 1926.

J. w. JAKEMAN SHEET GRIPPER MECHANSM OF PRINTING MACHINES Filed Feb. 51925 3 Sheets-Shaet 2 June 22 1926.

^ J. w. JAKEMAN SHEET GRIPPER MEcHANIsM oF PRINTING MAcHxNEs Filed Feb.5, 1925 3 Sheets-Sheet 3 17a/672m v i7 f J ,dwg/@f Patented June v22,1926.

UNITED STATES PATENT OFFICE.

JOHN WALLACE J'AKEMAN, OF ALTRINCHAM, ENGLAND, ASSIGNOR TO LINOTYPE ANDMACHINERY LIMITED, OF LONDON, ENGLAND, A BRITISH COMPANY.

SHEETGRIIPER MECHANISM OF PRINTING MACHINES.

Application filed February 5, 1925, Serial No. 6,924, and in GreatBritain February 19, 1924.

This invention relates to sheet-gripper mechanism such as that used inconnection with the impression cylinders of printing machines, whereinthe sheet grippers are secured to a shaft mounted in bearings iii thecylinder, and means are provided for rocking the shaft to open and closethe grippers at appropriate times during` the rotation of the cylinder.It'particularly relates to the known construction in which the springpressure is applied to a cain fast to the gripper shaft and isdirectedalong a straight line and serves both to supply the necessarygripping pressure .between the Agrippers and the sheets, and to hold thegrippers open and closed when the shaft is not under the influence ofthe mechanism by which it is rocked.

In one arrangement of this kind, the cam is so shaped that the pressureof the spring is directed against the cam along a line at substantiallyright angles to a radial line from Ythe axis ofthe gripper shaft, andthe operative portion of the cam is entirely concentric with the shaftexcepting where there are provided recesses with which a roller, underthe action of the spring, engages in order to lock the giippers in theiropen and closed positions.

The object of the present invention is to employ more advantageouslythan has been possible Vwith the means heretofore available, the forcesoperating during the action of the mechanism, so that springs, lighterthan those hitherto used for a corresponding gripper pressure, may beemployed with a corresponding reduction of friction load `on the grippershaft bearings, the shaft-rocking mechanism being thereby enabled tooperate more effectively and with less shock, While any tendency todisturb the cylinder by retarding or accelerating its rot-ation, isminimized and a higher ruiming speed of the press rendered possible.

With these objects in View, the present inveiition contemplates theemployment of a spring which exerts a force substantially radiallytowards the gripper shaft, in conjunctionA with means which resolve suchforce into components one of which exerts on the gripper shaft a turningmoment which decreases rapidly as said shaft is rocked to open thegripper-s and immediately there-V after possesses a gradually varyingvalue corresponding to some predetermined curve of moments and jus-tsufficient to complete, or assist in completing, the rocking of thegripper shaft vto retain thek grippeis open.

The invention will now be described by lFigure 4 is afsect-ional view-of part of the mechanism as seen from the left of Figure 2, and Y 1Figure 5 is a diagram illustrative of typical curves of spring momentsforthe hitherto used Slider-crank mechanism and the camact-iiatedmechanism according to the present invention, these being representedrespectively in full and dotted lines.

In the constructional form ofthe invention'excniplified in the drawings,the gripper shaft l, is rocked, in .the well-known manner by a tumblercam 2 rigidly attached to an outwardly extendingv end of said shaft, andkadapted by its cam recesses 3, 4, torenygage respectively with thestuds (not shown) for opening "and closing the gripper, which studs are,as ordinarily, moved axially into and out of their respectivetumbler-engaging positions.

5 is one of the several grippers which are adjustably secured on thelgripper shaft l, 6 is the gripper pad appropriate to that gripper, and 7vthe gripper pad shaft; the said pad and shaft are of any? suitableknown construction and, as they constitute no part of the invention, nofurther ydescription Vthereof is considered necessary.

The gripping pressure is imparted to the giippers 5 through, preferably,two bentlever arms Seach of which is pivoted, at one end,'as by ashouldered bolt 9, to one of the internal webs l0 of the impressioncylinder 1.1, and at the other or free end, as by a stud 12, to a springrod 13 which is encircled by a helical spring 14. rlhe spring rod 13,whose axis is virtually radial relatively to that of the gripper shaftl, is free to slide axially through a partly spherical washer 'l5 whichnests in a corresponding partly spherical seating formed in an eye-bolt16 rigidly secured to the appropriate cylinder web 10, While, near itsotherwise free end, it is provided With a collar 17 adjustable thereonand bet-Ween which and the Washer 15, the spring 14 exerts its pressure.

Each of the lever arms S is forked at its free end, and between thetines receives not only the end of the respective spring rod 13 but alsoa roller 18 which is free to rotate upon the respective stu-d 12. underthe influence of the respective spring 14, is caused to bear constantlyagainst a cam 19 rigidly secured to the gripper shaft 1.

The desired variations in the turning moment exerted by each spring 111on the gripper shaft 1 during the rocking of the latter, are secured bythe shape of the cam 19 on which the respective roller 18 bears, and thecam may be designed to give the desired gripping pressure When thegrippers 5 are closed and to ensure that, when the tumbler cam 2 engagesthe gripper opening stud, the

yforce of the springl 14 opposing the rocking of the shaft Will decreaserapidly. rlhe shape of the cam 19 further ensures that, during theopening of the grippers, the spring moment, on passing the zero point,that is to say the point in the cycle of operations at which the momentassumes Zero value, Will reach a value just suj'iiicient to overcome thefriction of the gripper shaft 1 in its bearings and to bring the tumblercam 2 into contact With a stop (not shown in the drawing) whichdetermines the opening movement of the grippers 5. Consequently, whenthe grippers are closing, the force opposing the action of the tumblercam 2 and the griliiper-closing stud, Will be small at the moment Whenthese members come into engagement and thereafter through thecompression of the spring, this force gradually increases up to a pointat which it changes in direction to assist the rocking of the grippershaft 1, after which the force increases rapidly to the maximum when thegripl'iers are closed.

In the constructional form illustrated, each cam 19 is provided With anabutment EEO with which the respective roller 1S ento retain thegrippers in their closed position.

The advantages derived from the present invention over and aboveexisting methods will best be appreciated from an inspection of theaccompanying diagram (Figure 5)., which shows by the full line a typicalcurve of spring moments for the usual slider-crank mechanism and by thedotted line y a similar curve of spring moments for the cam-actuatedmechanism according to the invention. 1n this diagram the ordinatesrepresent the moment of the spring and the abscissae angulardisplacementof This roller 18, Y

the gripper shaft from one of its extreme positions. The actual shape ofthe curve depends upon the following factors (i) The length of thespring lever or crank;

(ii) The stiffness or load per unit deflection of the spring;

(iii) The accumulation ratio i. e. the ratio of the initial load to thefinal load to the spring;

(iv) The ratio of the length of the crank to that of the spring rod, and

(v) The angle between the centre line of the crank and the line of deadcentres When the gripper shaft is in one of its extreme positions.

rissuming that the item (v) is half the total angular movement of thegripper shaft, the area under the curve above the line of abscissae isequal to the area ofthe curve below that line and is av minimum whenitems (i), (ii) and (iv) are small and item (iii) approachesy unity; thecurve then approximates 'to a curve of sines. The area-of the curveabove the line of abscissae represents to some sca e the Work done bythe gripper opening stud on the tumblercam in overcoming the moment ofthe spring, such work tending to retard the rotation of the cylinder;the area below the line of absciss represents to the saine scale theWork done by the spring in assisting the rotation of the gripper shaft,such Work tending to accelerate the rotation of the cylinder by reactionbetween the tumbler-cam and the gripper opening stud. The spring momentat the point X Where the grippers re closed is the same for bothmechanisms. The shaded area between the curves and 1/ showsthe saving ofWork and consequent Wear upon the tumbler-cam and the studs effected bythe employment of the mechanism according` to the present inventioninstead of the slider-crank mechanism heretofore employed for thepurpose.

To further elucidate the invention, it may be explained that the designof the cam 19 involves the following principle.

In any position of the mechanism, there are three forces meeting at apoint which is the centre of the cam roller 18.

These three forces are:.-

(1) The spring pressure acting along the line of the spring rod 13;

(i2) The pressure in the lever 8 acting along the line joining thecentres of the cam roller 18 and the fulcrum pin 9, and

The reaction between the cam 19 and cam roller 18 acting along the linejoining the centre of the cam roller to the centre of curvature of thecam at the point of contact.

Vhen the directions of three such forces and the magnitude of one ofthem are knovvn, the magnitudes of the other two forces can bedetermined.

fil

Further, the momentacting on the gripper shaft 1 is the product of thereaction between the cam 19 and its roller 18 into the vertical distanceof the line of action of this force from the centre of the grippershaft.

The object attained by a cam designed on this principle is to malte boththe magnitude of the reaction between the cam 19 and its roller 18 andthe vertical distance of its line of action from the centre of the shaft1 fall olf rapidly Vas the latter turns from t-he position shown inFigure 2, so that the curve of moments approximates to somepredetermined shape such as y in Figure 5.

Having described my invention, I declare that what I claim and desire`t0 secure by Letters Patent is 1. The combination with a printing presscylinder, a gripper shaft rmounted in said cylinder and adapted to berocked, sheet grippers carried by the gripper shaft adapted to be openedand closed by the rocking of that shaft, and a spring adapted to exertva force substantially radially towardsl the gripper shaft, of meansadapted to resolve such force into components one of which exerts on thegripper shaft a turning moment which decreases rapidly as said shaft isrocked to open the' grippers and immediately thereafter possesses agradually varying value corresponding to some' predetermined curve ofmoments and just sufficient to complete, or assist in completing, therocking of the gripper shaft to retain the erippers open.

2. The combination with a printing press cylinder', a gripper shaftmountedrin said cylinder and adapted to be rocked, sheet gripperscarried by the gripper shaft adapted to be opened and closed by therocking of that shaft, and a spring adapted toeXert a forcesubstantially radially towards the gripper shaft, of means adapted toresolve such force into components, one of which exerts a turning momenton the gripper shaft said means comprising a cam so formed that thecomponent exerting the turning moment acts through the cam along a linethe perpendicular distance of which from the centre oi' the grippershaft d ecreases rapidly as said shaft is rocked to open the grippersand throughout the re-V mainder of the grippenopening movement graduallyvaries until the turning .moment is just sufficient to complete orassist in completing the rocking of the gripper shaft to retain thegrippers open.

, 3. The combination with a printing press cylinder, of a gripper shaftmounted in said cylinder and adapted to be rocked, sheet gripperscarried by the gripper shaft adapted to be opened and closed by therocking of that shaft, a spring adapted to exert a force substantiallyradially towards the gripper shaft, a cam mounted onthe gripper shaft, alever arm having one end pivoted to the impression cylinder, a rod towhich the other end 0f the leverarm is pivoted and a roller carried bysaid rod and constantly held by the spring in contact with the cam, saidcam being so formedV that the perpendicular distance of the line ofaction of the force between the cam and roller'decreases rapidly as thegripper shaft is rocked to Open the grippers, and throughout theremainder of the gripper-opening` movement gradually varies until theturning moment is just sullicient to complete or ,assist in completingthe rocking of the gripper shaft to retain the grippers open.

.4. The combination with a printing press l cylinder, a gripper shaftmounted in said cylinder adapted to be rocked, and sheet gripperscarried by the gripper shaft adaptyed'to be opened and closed by therocking of that shaft, of a cam mounted on the gripn per shaft, a leverarm having one en pivoted to the impression cylinder, an axiallyslidable rod to which the other end of the lever arm is pivoted, andWhose axis is virtually radial relatively to that of the grippershaft, aroller carried by said rod, and

a spring encircling said rod and constantly holding said roller incontact with the cam, said cam being so formed that the perpendiculardistance of the line of action of the force between the cam and rollerdecreases rapidly as the gripper shaft is rocked to open the grippers,and throughout the remainder of the gripper-opening movement graduallyvaries until the turning momentV is just sufficient to complete orassist in completing the rocking of the gripper shaft to retain thegrippers open.

In testimony whereof signature hereto.

JOHN WALLACE JAKEMAN,

I have aixed my

